In recent year, a solar cell (solar cell module) has been widely employed as a device directly converting solar energy into electric energy from the viewpoints of effective use of natural resources and ecology. Further development of solar cells is in progress.
As shown in FIG. 1, a solar cell generally includes a transparent front side protection material 11 (e.g., glass plate), a front side sealing film 13A, plural photovoltaic elements 14 (e.g., photovoltaic elements made of silicon), a backside sealing film 13B and a backside protection material 12 (backside covering member). For preparing a solar cell, first, the foregoing members are successively laminated in this order. Then, the laminated body is subjected to vacuum degassing, subsequently, heating under pressure for adhesively combining the laminated body by crosslinking or curing a front side sealing film 13A and a backside sealing film 13B. A conventional solar cell has connected plural photovoltaic elements 14 for generating a large electrical output. In order to ensure an electrical insulation property, plural photovoltaic elements 14 are sealed through a front side sealing film 13A and a backside sealing film 13B, which have high insulation properties.
Films made of ethylene-vinyl acetate (EVA) are used as sealing films in conventional solar cell because of low cost and high transparency. Furthermore, it is required that an EVA film used in sealing films is combined with members of a solar cell with keeping high adhesive strength, in order to ensure mechanical durability of the solar cell, and prevent internal electrical leads and electrodes from rust caused by humidity or permeated water.
For this reason, in the conventional solar cell sealing film, addition of organic peroxides as crosslinker to EVA gives crosslinked structure to improve weather resistance, and furthermore, addition of silane-coupling agents to EVA brings about the improvement of adhesive strength (Patent Document 1).